Peroxyl Radicals - Free-Radical-Induced DNA Damage and Its Repair - page 158

The autoxidation of polyunsaturated fatty acids (cf. Porter et al. 1981) is usually
monitored by the formation of “malonaldehyde” using the 2-thiobarbituric acid
essay. This is carried out under rather severe conditions which decomposes its
precursor. This malonaldehyde-like product is obviously formed via a cycliza-
tion reaction of a peroxyl radical, followed by other processes such as further
cyclization and hydroperoxide formation [reactions (21)−(23)]. The resulting
hydroperoxides may eliminate malonaldehyde upon a homolytic cleavage of the
endoperoxidic intermediate (Pryor and Stanley 1975).

OOH

OOH

In the series of hydroxycyclohexadienylperoxyl radicals, one encounters the
competition between the HO 2 • /O 2 • − elimination leading to phenol [reactions (9)
and (14)/(15)] and fragmentation of the ring (Pan et al. 1993). That latter has
been attributed to an intramolecular addition of the peroxyl radical function to
a diene double bond [reaction (24)]. This reaction is reversible [reaction (

24)],
but when O 2 adds to the newly created carbon-centered radical the endoperoxid-
ic function is locked in [reaction (25)]. In analogy to reaction (24), the first step
of the trichloromethylperoxyl-radical-induced oxidation of indole is its addition
to the indole C (2)

−

− C (3) double bond (Shen et al. 1989).